Neuro-Ophthalmology and Neuro-Otology
Proper examination of the oculomotor system provides the most localizing and diagnostic “bang for the buck” than that of any other system.
Saccadic impairment alone brings attention to supranuclear eye movement disorders, since nuclear and infranuclear lesions impair saccades, pursuit, and vestibular eye movements equally.
Any motility disorder that does not involve the pupil should include myasthenia gravis and Miller Fisher syndrome (ophthalmoplegia, ataxia, and areflexia) in the diagnostic considerations.
Any motility disorder, especially if diffuse, that involves the pupil (mydriasis) should always include botulism among the considerations.
Eye deviated down and out with impaired adduction, supraduction and infraduction, eyelid ptosis, and mydriasis: internal carotid-posterior communicating artery junction aneurysm causing third nerve palsy until proven otherwise.
Same as above but with normal pupil (pupil sparing): ischemic cranial neuropathy resulting from diabetes or hypertension.
Vertical diplopia has a narrow differential: CN IV (trochlear) palsy or skew deviation from a brainstem stroke.
In the presence of CN III palsy, the method of testing CN IV palsy by asking the patient to depress the adducted eye cannot be performed. Instead, the patient should be instructed to abduct the eye and then look down; if CN IV is intact, there will be intorsion. Confirming that CN IV is intact in the presence of CN III palsy is important because the combination of a CN III and CN IV palsy suggests a lesion in the cavernous sinus. Caveat: Pupil sparing partial CN III palsies may progress to involve the pupil and are related to compressive lesions.
Horizontal gaze palsy from an abducens nuclear lesion occurs rarely in isolation. Most often, it is accompanied by an ipsilateral facial nerve palsy because the seventh nerve fascicle wraps around the abducens nucleus.
When dizziness is central (brainstem or cerebellar stroke), there is a normal vestibulo-ocular response (as measured by head impulse test), direction-changing nystagmus, and vertical strabismus on alternating covering of the eyes (skew deviation).
When dizziness is peripheral (acute vestibulopathy), there is an abnormal vestibulo-ocular response, nystagmus beats in the same direction regardless of direction of gaze, and there never is skew deviation.
“Peering at the tip of the nose” from supranuclear gaze palsy with forced downward deviation of the eyes may be due to a thalamic lesion, which can also cause “supranuclear thalamic esotropia,” probably secondary to excessive convergence tone.
Cerebral polyopia is a form of cortical visual perseveration from parieto-occipital pathology. It refers to two or more visual images persistent with monocular covering, and often accompanied by a homonymous hemianopia.
Transient Monocular Visual Loss
Transient monocular visual loss (TMVL) results from hypoperfusion (amaurosis fugax) or disc pressure (transient visual obscurations),
Amaurosis fugax (retinal TIA) expresses as a painless dark or black shade or “gray-out” that suddenly spreads across the visual field and lasts a few minutes. Positive visual phenomena and visual worsening with exposure to bright light also suggest ocular hypoperfusion. It represents the most helpful localizing sign of carotid steno-occlusive disease. Funduscopic examination may show emboli to the retinal circulation or multiple peripheral dot-blot hemorrhages consistent with venous stasis retinopathy.
Amaurosis fugax on exposure to bright light is often associated with severe ipsilateral carotid artery occlusive disease. Patients with amaurosis fugax have a lower risk of subse-quent stroke than those with TIAs involving the brain.
The risk of stroke in patients with TMVL and ipsilateral significant carotid stenosis is less than half of those with hemispheric TIAs. The risk of death in patients with TMVL and atheromatous carotid stenosis is approximately 4% per year.
Nonvascular TMVL
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Transient visual obscurations are briefer (usually lasting seconds) TMVL due to elevated intracranial pressure (ICP) from increased pressure at the optic nerve head precipitated by postural changes, such as bending over. It is associated with papilledema but with normal visual acuity, enlarged blind spots, and visual constriction. Neuroimaging is indicated to explore the causes of raised intracranial pressure (mass lesions, hydrocephalus, or cerebral venous thrombosis). Negative imaging should be followed by a lumbar puncture to confirm the presence of elevated ICP and to analyze the CSF for evidence of meningeal inflammation. Elevated ICP in the presence of normal imaging and CSF studies meet criteria for idiopathic intracranial hypertension.
Migraine may rarely present as TMVL (ocular or retinal migraine). Episodes may last minutes to hours and may be followed by headache or ocular pain in young, healthy people. They build up over time and are associated with scintillations and other positive visual phenomena.
Permanent Monocular Visual Loss
Permanent monocular visual loss (PMVL) results from lesions anterior to the chiasm (eye itself or optic nerve).
Acute PMVL (vascular) stems from occlusion of the ophthalmic artery or, more often, either of its two terminal branches (central retinal and posterior ciliary).
 Posterior ischemic optic neuropathy (PION) refers to the rare involvement of the retrobulbar segment of the optic nerve occurring in the setting of severe and prolonged arterial hypotension. |
Anterior ischemic optic neuropathy (AION) results from damage to the optic nerve head from occlusion of branches of the posterior ciliary artery.
Nonarteritic AION is characterized by an acute painless altitudinal defect (often inferior). Disc edema may be segmental (often superior). The risk factors are hypertension, diabetes, and congenitally small optic nerve heads (no physiologic cupping or “crowded” disc: small cup-to-disc ratio).
Arteritic AION is the most common manifestation of giant-cell arteritis (GCA) in those older than 50 years and may be predated by episodes of painful diplopia and TMVL. The fellow eye can deteriorate within days or weeks.
Central retinal artery occlusion (CRAO) typically causes acute painless loss of vision and diffuse retinal whitening with foveal sparing (choroidal circulation), creating the classic macular cherry-red spot. Painful CRAO may result from carotid dissection (especially when present with ophthalmoparesis or Horner syndrome) or GCA. Treatments include lowering the IOP pressure (acetazolamide), anterior chamber paracentesis, and ocular massage. The role of thrombolytic therapy is unknown.
Progressive forms of PMVL are the result of unilateral optic neuropathies from infiltrative or compressive pathologies such as optic nerve gliomas, optic nerve sheath meningiomas, pituitary tumors, or sarcoidosis.
Acute or Subacute MVL in a Younger Patient: Optic Neuritis
Optic neuritis (ON) is characterized by subacute visual loss associated with retro-orbital or ocular pain, worse with eye movements. The earliest findings are relative afferent pupillary defect (RAPD), reduction in color saturation, and central scotoma. The optic disc may be swollen (prebulbar ON) or normal (retrobulbar ON). Visual loss worsens with heat or exercise (Uhthoff phenomenon).
RAPD or Marcus Gunn pupil is seen in unilateral or asymmetric optic neuropathy. Both pupils constrict less when the affected eye is illuminated and more when the normal eye is shone. Neutral density filters placed over the normal eye can help quantify its severity.
Retrobulbar ON is diagnosed when the above deficits occur in the setting of normal funduscopy (“the patient sees nothing and the doctor sees nothing”). Vision recovers over several weeks, but optic disc pallor appears (“the patient sees everything and so does the doctor”).
Differential Diagnosis of Inflammatory Optic Neuritis
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Idiopathic ON is the most common acute optic neuropathy in people younger than 45 years with spontaneous visual recovery within 3 weeks in 80% of patients. The risk of MS after ON is 16% at 5 years and as high as 75% at 15 years. The 10-year risk of MS is 56% in patients with ≥12 MRI T2W lesions, compared to 22% with a normal baseline MRI. A very low MS risk comes from the combination of painless ON and normal brain MRI, optic nerve edema, peripapillary hemorrhages, or a macular star. Predictive factors for the development of MS include Caucasian ethnicity, family history, female gender, retrobulbar ON, pain, and CSF oligoclonal bands. IV methylprednisolone (250 mg four times daily for 3 days), followed by oral prednisone (1 mg/kg/d) for 11 days, hastens the rate of recovery of vision. Oral prednisone is associated with an increased risk of recurrent ON. Although high-dose IV methylprednisolone speeds recovery, it does not improve the final outcome. Initiation of treatment with beta-interferons and glatiramer acetate at the time of a first episode of ON in patients at high-risk for MS lessens the number of new and active MS lesions on MRI and the number of clinical relapses, and appears to slow the progression of neurologic impairment.
Binocular Visual Loss
Persistent binocular visual loss (PBVL) results from damage to both optic nerves, the chiasm, or the retrochiasmal visual pathways. Chiasmal and retrochiasmal lesions respect the vertical meridian. Visual acuity is affected (symmetrically) only on bilateral retrochiasmal lesions involving the foveal nerve fibers on both sides. Blindness of cerebral origin preserves the pupillary light reflex.
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Optic neuropathies due to mitochondrial (Leber hereditary optic neuropathy), toxic (methanol, tobacco, lead, amiodarone, disulfiram, chloroquine, ethambutol, isoniazid), or nutritional deficiencies (vitamins B1, B2, B3, B6, and B12) are symmetric and progressive PBVL. Patients often present with painless, bilateral, symmetric visual impairment, dyschromatopsia, swollen or hyperemic discs in the early stages, followed by variable degree of optic nerve head pallor. The classic visual field defect is a cecocentral scotoma. The most common bilateral optic neuropathy in the Western world is primary open-angle glaucoma.
Transient binocular visual loss (TBVL) is most commonly part of the visual aura that occurs with ophthalmic migraine. An episodic and brief (over minutes) enlarging scotoma in homonymous portions of the visual field is surrounded by jagged, shimmering lights and is followed by contralateral hemicranial throbbing headache. Absence of the latter is more common after the age of 50 (acephalgic migraine or migraine equivalent). TIAs in the vertebrobasilar territory may cause TBVL, which, unlike migraine, begin suddenly with concurrent pain above the contralateral brow and lack positive phenomena or stereotypical build-up.
Cerebral Visual Loss
Besides the retinogeniculostriate (topographic; yielding specific field hemifield defects outlined above) component of visual information, two “higher level” visual streams are described as part of the secondary or association visual cortical areas: the occipitotemporal or ventral “what” pathway of object identity, such as form and color, and the occipitoparietal or dorsal “where” visual pathway of motion, stereopsis, and spatial location. Diffuse lesions in both occipital lobes or both optic radiations lead to Anton syndrome, complete cerebral blindness with denial of blindness and confabulation.
Major Causes of Cerebral Visual Loss
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Occipitotemporal Disorders (Ventral Extrastriate Region): Object Recognition
Achromatopsia from lesions of the contralateral lingual and fusiform gyri; bilateral lesions make patients only see “dirty shades of gray”
Object agnosia, from lesions in both medial temporal lobes, consists of inability to name and describe objects until other sensory modality is used
Alexia without agraphia from lesions in the left visual cortex (which causes right homonymous hemianopsia) and splenius of corpus callosum
Alexia with agraphia from lesions in the left angular gyrus and left occipitotemporal cortex
Prosopagnosia or inability to recognize faces, from bilateral or right medial temporal lesions
Topographagnosia or geographic disorientation, from right medial occipitotemporal cortex lesions
Occipitoparietal Disorders (Dorsal Extrastriate Region): Object Localization
Balint syndrome, caused by bilateral occipitoparietal lesions, consists of simultanagnosia (inability to interpret a complex scene with multiple interrelated elements despite accurate “piecemeal” description), ocular apraxia (psychic gaze paralysis leading to difficulty initiating saccades), and optic ataxia (disturbance of visually guided reaching behavior caused by difficulty in judging the spatial position of objects—visual disorientation)
Hemineglect or a spatially based failure of attention caused by lesions in the right parietal lobe
Akinetopsia or impairment of motion perception leading to misjudgment of speed and direction of moving objects, from bilateral occipitoparietotemporal lesionsRelated posts:
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